CHICAGO — Last week the Chicago Bears showed fans what their new defense was supposed to look like in a preseason-opening win over Philadelphia.

On Thursday night, they took a little step back, but still managed to haul in a 20-19 come-from-behind victory over Jacksonville in the second preseason tilt. And luckily for the Bears’ defense, there is not only plenty of time to correct the mistakes, but they are also clearly fixable — unlike the situation around this time last season.

“I like where our team is headed,” new defensive end Jared Allen said. “But we just have to watch the film and clean up some little details.”

Allen got his first action as a Bear on Thursday, nearly getting a sack while disrupting things in the backfield on four different occasions. And low and behold, even Shea McClellin made a play from his new linebacker slot, slashing into the backfield for a tackle for a loss early in the first half.

“He’s seeing things a little bit differently, but Shea’s real smart, and he’s very athletic,” linebacker Lance Briggs said. “The thing about him in practice, and even tonight in the game, he’s always around the ball.”

And in the end, the Bears only surrendered 19 points.

But the defense as a whole was not good, especially early on. In four of their first five scoring drives, the Jags settled for field goals. But that all came in just over two quarters — which means Jacksonville had five scoring drives in just over a half. Yes, that Jacksonville.

And for a team that does not believe in the old bend-but-don’t-break motto, that just won’t do.

“No, no, that’s not in my NFL pedigree,” safety Ryan Mundy said. “That’s not how we do it. That’s not our mindset here at all. We want to be a great defense; this is a defensive city, and there’s a lot of tradition and history on this defense. And we have to live up to that. We’re excited about that challenge and opportunity.”

The Jags chipped away and nickel-and-dimed the Bears to death, and should’ve gotten the win for it. But Jordan Palmer hit Ka’Deem Carey across the middle and then Senorise Perry along the sideline to put the Bears into the end zone late to turn it around.

Still, they trailed from the get-go, and even the come-from-behind victory didn’t erase the defensive deficiencies that stuck out early.

Page 2 of 2 - A lot of the problems came against the pass, too, where Chicago’s coaching staff continued to rotate safeties in and out, searching desperately for a winning combo.

The first safety tandem of the night, Mundy and Danny McCray, was not good. Jacksonville’s no-name attack picked them apart.

The second grouping of Adrian Wilson and Brock Vereern? A little better. By the time M.D. Jennings and Marcus Trice made it onto the field, not many fans were paying attention. I was. They were also not very good.

A couple of guys who made strong cases for more regular-season playing time Thursday were wideouts Chris Williams and Marquess Wilson, defensive lineman Willie Young and safety Chris Conte. They did not suit up to play in this one, thus they did not mess anything up.

And new No. 2 quarterback Jimmy Clausen was decent, going 11-for-15 for 94 yards. The guy now pushing him, Palmer, kept the pressure on by going 6-for-9 for 73 yards while leading the Bears down the field for the game-winner with just under a minute left. And keeping the positives on the offensive side, rookie running back Carey burst for a 15-yard run to set up a 1-yard, fourth-quarter touchdown run that made it a game down the stretch.

But the defense looked a lot like it did last year as it allowed the Jags to run away early.